Inverters, which are typical examples of power converters, are necessary components for controlling driving motors for hybrid and/or electric vehicles. Such an inverter includes upper- and lower-arm switching elements, each of which is preferably an insulated gate bipolar transistor (IGBT). Alternately turning on and off each of the IGBTs of the inverter converts DC power supplied from a DC power source into AC power. Alternately turning on and off each of the IGBTs of the inverter also converts AC power generated from a rotary electric machine into DC power.
For turning on or off each of the IGBTs of the inverter, a power supply circuit is used, one example of which is disclosed in Japanese Patent Application Publication No. H11-178356.
Such a power supply circuit is implemented in a board, and is connected to each IGBT of the inverter. The power supply circuit includes a gate driver and a transformer for each IGBT. The gate driver for each IGBT controls on or off of the corresponding IGBT. The transformer for each IGBT supplies power to the corresponding gate driver. The transformer for each IGBT includes a primary coil and a secondary coil magnetically coupled to the primary coil.
The power supply circuit also includes a power controller commonly provided for individually controlling all the IGBTs. The power controller includes a voltage-controlled switching element, such as a MOSFET, connected to the primary coil of each transformer.
Alternately turning on and off the voltage-controlled switching element alternately switches between a first mode supplying a current to the primary coil and a second mode interrupting the supply of the current to the primary coil. This current-control controls the operating state of each gate driver connected to the primary coil of a corresponding one of the transformers, thus controlling the switching operations of the IGBTs of the inverter.